Make tls_version_max return the actual maximum version

Make tls_version_max return the actual maximum version

Before OpenSSL 1.1.1 there could be no mismatch between
compiled and actual OpenSSL version. With OpenSSL 1.1.1 we need
runtime detection to detect the actual best TLS version supported.

Allowing this runtime detection also allows removing some of the
TLS 1.3/OpenSSL 1.1.1 #ifdefs

Without this patch tls-min-version 1.3 or-highest will actually
downgrade to TLS 1.2 in the "compiled with 1.1.0 and linked against
1.1.1" scenario.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20191122143315.8564-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg19186.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>